Method and apparatus for cathodically protecting reinforced concrete structures

ABSTRACT

Galvanic protection of a reinforced concrete structure or a metallic structure immersed or partially immersed in water or seawater utilizes a sacrificial anode having a more negative electrode potential than that of the metal to be protected but connected to the reinforcement or metallic structure, and the anode immersed in electrolyte solution creating an corrosive environment for the anode. The electrolyte solution must exist for internal charge transfer by ionic conductance, and to complete the electric circuit of the galvanic cell therefore both the metal or reinforced structure and the sacrificial anode have to be immersed in an electrolyte solution. The anode will provide in that way sufficient current to protect the reinforcement or metal structure against corrosion. The present invention resides in a method where the sacrificial anode immersed in an electrolyte solution can be positioned on a remote location e.g. in a small container away from the reinforced concrete or metal structure. This is done in a manner that both electrolyte solutions in which one electrolyte solution the metal or reinforced structure is immersed and second electrolyte solution the anode is immersed are connected through two metallic non-corrosive current distributors providing an electrical bridge between both electrolytes.  
     The current density can be adjusted by increasing or decreasing the surface area of the current distributor immersed in the electrolyte solution in which the anode is immersed.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Method and Apparatus for Cathodically Protecting Reinforced Concrete Structures.

[0002] U.S. Pat. No. 5,292,411; Bartholomew, John J. ; Mar. 8, 1994; discloses a method for cathodically protecting a reinforced concrete structure by adhering a metal anode such as a zinc anode sheet to a surface of the concrete structure. A pressure sensitive coating of an ionically conductive hydrogel is on a surface between the anode and the concrete surface.

[0003] Relating to the Cathodic Protection of Structures

[0004] U.S. Pat. No. 4,078,510 ; Morgan, John Harold; Mar. 14, 1978; discloses a method of surveying a cathodically protected metallic structure at least partly immersed in a liquid, such as an undersea pipeline which has sacrificial anodes attached at regular intervals along its length. The potential differences in the water between a point adjacent an anode, and test points adjacent the pipeline are measured, and the varying level of protection along the pipe is determined from the variations between the measured potential differences.

[0005] Method for Preventing Corrosion of a Reinforced Concrete Structure

[0006] U.S. Pat. No. 5,341,562 ; Furuya, Akio ; Aug. 30, 1994; discloses a method for preventing corrosion of a reinforced concrete structure having a reinforcing steel embedded therein, which comprises coating an aggregate-containing primer on the surface of the reinforced concrete structure, to form a primer layer having a rough surface, metal-spraying a metal having an ionization tendency larger than iron on the primer layer to form a metal spray coating layer, and connecting the metal spray coating layer and the reinforcing steel by an electrically conductive material.

[0007] Galvanic Protection of Rebar by Zinc Wire

[0008] U.S. Pat. No. 5,449,563 ; Zhang, Xiaoge G. ; Sep. 12, 1995: discloses a method for preventing corrosion of a reinforced concrete structure by attaching a zinc wire, such as by welding, soldering or co-extrusion, along the length of the rebar. Zinc wire attached to the rebar provides galvanic protection to the steel to prevent iron corrosion and subsequent deterioration of the reinforced concrete.

[0009] Cathodic Protection System for Reinforced Concrete

[0010] U.S. Pat. No. 5,968,339 ; Clear, Kenneth C.; Oct. 19, 1999; resides also in a cathodic protection system of reinforced concrete which comprises a conductive corrodible metal anode positioned at a point remote from the surface of the concrete structure. An electric circuit connects the anode and the reinforcement of the concrete structure. A current distributor positioned on a surface of the concrete structure is connected to the anode by a salt bridge. The salt bridge preferably is a capillary tube that is filled with an ionically conductive fluid and/or solid material. The salt bridge extends into the container with the electrolyte solution in contact with the anode and connects the anode with the current distributor.

BACKGROUND OF THE INVENTION

[0011] The present invention relates to a method and apparatus for galvanically protecting reinforced concrete structures, such as the decks or substructures of bridges, wharfs and parking garages and steel or metal structures immersed or partially immersed in water or seawater or any other electrolyte solution, such as off-shore platforms and structures or seagoing vessels.

[0012] Anodes for use in applications as mentioned in the introduction are used to prevent corrosion on the surface of the reinforcement of concrete structures and other various steel or metal structures, exposed to an ionically conducting medium. They comprise an active current transferring surface, which is in electric contact with the medium and which transfers a direct current between that surface and the surface of the structure, through the medium. The current influencing the corrosion processes is transferred between the electrode and the structure via the ionically conducting medium.

[0013] As can be understood from the patents mentioned in the references cited, where a galvanic cell is used it is important that the electrolyte contacting the anode is such that sustained active corrosion of the anode can occur and that the electrolyte must also be in contact with the surrounding concrete for internal charge transfer by ionic conductance, and to complete the electric circuit. Salt bridges as ionically conductive fluids and/or solid materials as described in the above mentioned patents are known for decades within the field of electrochemistry and used in several applications.

[0014] However, a disadvantage of salt bridges as an ionically conductive material applied in galvanic cells is the increasing electric resistivity by increasing the distance of the anode and the metal structure being protected. The use of salt bridges will therefore limit the distance between the anode and the structure being protected.

[0015] The present invention will overcome this limitation by replacing the salt bridge by two current distributors, and both connected to each other with an electric or metal conductor or circuit such as cupper wire.

BRIEF SUMMARY OF THE INVENTION

[0016] The present invention resides in a method for galvanically protecting of a reinforced concrete structure or steel or metal structure immersed or partially immersed in water or seawater or any other electrolyte solution of which the sacrificial anode immersed in an electrolyte solution can be positioned on a remote location e.g. in a small container away from the reinforced concrete or steel or metal structure. This is done in a manner that both electrolyte solutions in which the electrolyte solution the metal or reinforced structure is immersed and the other electrolyte solution the anode is immersed are connected through two metallic non-corrosive current distributors providing an electrical bridge between both electrolytes.

[0017] The sacrificial anode is immersed in an electrolyte solution having a pH which is maintained sufficiently high for corrosion of the anode to occur and for passive film formation on the anode to be avoided. The anode material selected will determine the electrolyte pH required to maintain active corrosion.

[0018] The anode is preferably zinc or a zinc alloy but the anode may be aluminium, an aluminium alloy, cadmium, a cadmium alloy, magnesium or a magnesium alloy or another material which has a more negative standard electrode potential than the reinforcement of concrete or steel or metal structure immersed or partially immersed in water or seawater or any other electrolyte solution under the prevalent conditions.

[0019] The electrical connection which is replacing the salt bridge used in galvanic cells to seperate the electrolyte solution consists of two metallic non-corrosive current distributors and both connected to each other with an electric or metal conductor or circuit such as cupper wire.

[0020] The current distributors are preferably non or low corrosive electric conductive materials such as Platinum, Carbon, Stainless Steel or activated Titanium.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

[0021]FIG. 1 is a perspective view of the basic invention of which the following numbers represent:

[0022] 1 electrolyte solution

[0023] 2 sacrificial anode

[0024] 3 current distributor

[0025] 4 electric lead

[0026] 5 electric lead

[0027] 6 current distributor

[0028] 7 electrolyte solution

[0029] 8 steel or metal structure

[0030]FIG. 2 is a perspective view of reinforced concrete protected in a manner of the present invention of which the following numbers represent:

[0031] 1 reinforced concrete stucture

[0032] 2 reinforcement

[0033] 3 current distributor

[0034] 4 electric lead

[0035] 5 electric lead

[0036] 6 container

[0037] 7 electrolyte solution

[0038] 8 sacrificial anode

[0039] 9 current distributor

[0040]FIG. 3 is a perspective view of a steel or metal structure immersed or partially immersed in water or seawater or any other electrolyte solution protected in a manner of the present invention in which the following numbers represent:

[0041] 1 electric lead

[0042] 2 steel or metal structure

[0043] 3 water or seawater or any other electrolyte solution

[0044] 4 electric lead

[0045] 5 container

[0046] 6 electrolyte solution

[0047] 7 sacrificial anode

[0048] 8 current distributor

[0049] 9 electric insulator

[0050] 10 current distributor

DETAILLED DESCRIPTION OF THE INVENTION

[0051] In the embodiment of FIG. 1, the galvanic cell comprises 2 containers with both an electrolyte solution 1 en 7. The first container comprises an anode 2 and a current distributor 3. The current distributor 3 is connected by a lead 5 with a similar metal current distributor 6 which extends into the electrolyte solution of the second container. A preferred lead 5 is a metallic conductor such as cupper wire which connects both current distributors 3 en 6. A preferred current distributor 3 is a non or low corrosive conductive material such as Platinum, Carbon, Stainless Steel or activated Titanium. An electric lead 4 connects the anode 2 directly with a metal structure 8 to be galvanically protected. A preferred lead 4 is a metal conductor such as cupper wire.

[0052] In the operation of this embodiment, the anode 2 is consumed by the electrolyte solution 1. This causes a current flow between the metal structure 8 and anode 2, via lead 4, which protects the metal structure 8.

[0053] In the embodiment of FIG. 2, the galvanic protection system comprises an anode 8 which is remote from the reinforced concrete structure 1. A current distributor 3 is positioned on the surface of the reinforced concerte structure 1. The current distributor 3 can be in the form of a metal mesh or conductive coating. The current distributor 3 is connected to a lead 4 which extends into a container 6. The lead 4 is connected with a metal current distributor which extends into the electrolyte solution. Anode 8 is positioned inside the container 6. The container 6 is filled with an electrolyte solution 7. A preferred lead 4 is a metallic conductor such as cupper wire which connects the current distributor 9 with the current distributor 3. A preferred current distributor 3 is a non-corrosive metal such as Platinum or activated Titanium An electric lead 5 connects the anode 8 directly with the reinforcement 2.

[0054] In the operation of this embodiment, the anode 8 is consumed by the electrolyte solution 7. This causes a current flow between the reinforcement 2 and anode 8, via lead 5, which protects the reinforcement.

[0055] An advantage of this embodiment of the present invention is that the anode 8 can be serviced and replaced without accessing that portion of the galvanic protection system physically attached to the concrete structure and can be positioned on a remote location in a container 6 on a great distance away from the reinforced concrete. Unlike a salt bridge the metallic conductor will have no distance limitations due to increasing resistivity.

[0056] In the embodiment of FIG. 3, the galvanic protection system comprises an anode 7 which is remote from a steel or metal structure 2 immersed or partially immersed in water or seawater or any other electrolyte solution. A current distributor 10 is positioned on a specific part of the surface of the steel or metal structure 2 which specific part of the surface is immersed in the water or seawater or any other electrolyte solution but isolated from the structure by an electric insulator 9. The current distributor 10 can be in the form of a non or low corrosive material such as Platinum, Carbon, Stainless Steel or activated Titanium. The current distributor 10 is connected to a lead 4 which extends into a container 5. The lead 4 is connected with a metal current distributor which extends into the electrolyte solution. Anode 7 is positioned inside the container 5. The container 5 is filled with an electrolyte solution 6.

[0057] A preferred lead 4 is a metal conductor such as cupper wire which connects the current distributor 10 with the current distributor 8. A preferred current distributor 8 is a non or low corrosive meterial such as Platinum, Carbon, Stainless Steel or activated Titanium. An electric lead 1 connects the anode 7 directly with the steel or metal structure 2.

[0058] In the operation of this embodiment, the anode 7 is consumed by the electrolyte solution 6. This causes a current flow between the steel or metal structure 2 and anode 7, via lead 1, which protects the steel or metal structure.

[0059] An advantage of this embodiment of the present invention is that the anode 7 can be serviced and replaced without accessing that portion of the galvanic protection system which is normally physically attached under water or seawater or any other electrolyte solution to the steel or metal structure, and can be positioned on a remote dry location in a container 6 on top or inside the steel or metal structure. A salt bridge can not operate in such an embodiment as the water or seawater will go easily through a capillary tube filled with an ionically conductive fluid due to the static pressure. 

What I claim as my invention is: 1) A method of galvanically protecting a reinforced concrete structure comprising the steps of: (a) electrically connecting a sacrificial anode to the steel reinforcement of the concrete structure, the anode having a more negative electrode potential than that of the steel reinforcement; (b) the sacrificial anode to be immersed in an electrolyte solution creating a corrosive environment for the anode, and providing in that way sufficient current to protect the reinforcement against corrosion; (c) the sacrificial anode immersed in an electrolyte solution being positioned on a remote location e.g. in a small container away from the reinforced concrete; (d) providing an electrical bridge between both the electrolyte solutions by electrically connecting the current distributor which is immersed in the electrolyte solution in which the anode is immersed and a current distributor applied on the surface of the reinforced concrete. 2) A method of galvanically protecting a steel or metal structure immersed or partially immersed in water or seawater or any other electrolyte solutions comprising the steps of: (a) electrically connecting a sacrificial anode to the steel or metal structure immersed or partially immersed in water or seawater or any other electrolyte solutions, the anode having a more negative electrode potential than that of the steel or metal structure; (b) the sacrificial anode to be immersed in an electrolyte solution creating a corrosive environment for the anode, and providing in that way sufficient current to protect the steel or metal structure immersed or partially immersed in water or seawater or any other electrolyte solutions against corrosion; (c) the sacrificial anode immersed in an electrolyte solution being positioned on a remote location e.g. in a small container away from the steel or metal structure immersed or partially immersed in water or seawater or any other electrolyte solutions; (d) providing an electrical bridge between both the electrolyte solutions by electrically connecting the current distributor which is immersed in the electrolyte solution in which the anode is immersed and a current distributor which is immersed in the water or seawater or any other electrolyte solutions in which the steel or metal structure is immersed. 